Fuse plug



Nov. 27, 1934. G. R. TRUMBULL FUSE PLUG Original Filed Dec. 4, 1930 bull,

George R INVENTOR Patented Nov. 27, 1934 UNITED STATES PATENT OFFICE FUSE PLUG necticut Application December 4, 1930, Serial No. 499,945 Renewed ctober12,.1933

11 Claims.

My invention relates to protective devices of the type employing'a fusible'strip or link. Such devices, of course, areused to protect circuits and apparatus'against prolonged overloads as well as against short circuiting.

Ithas been proposed to enclose the link in a housing, the front of which is transparent and through which the fuse link may be observed. It is thus possible to know at all times the condition of the link, and furthermore by marking the link'itself with its rating itis possible to use the same housingfor all ratings. It is especially desirable to form the housing, or at least the outer part of it; of glass which is'capable of being -molded in one piece and'has excellent electrical as well. as mechanical characteristics; It has been found, however, that such constructions are liable to fracture under certain conditions when the fuse blows. This introduces a hazardous element which is a serious objection to glass top fuse plugs;

I have discovered an extremely simple method or means for removing the hazard and at the same time retaining the advantages of the glass 'top, plug. In fact the invention is. applicable to constructions now on the market without requiring any modification of the same except the addition of the protective element.

I As an example of the invention I have illustrated one form of construction embodying an insulating base which supports the fuse link, a glass top which forms. in conjunction with the base a chamber for the fuse link, and a screw A shell which holds the parts together. The inte- 'rior of the plug is provided with a coating of a material such as water glass which is transparent and thereforedoes not interfere with the visibility of the linkthrough the top.

Fig. 1 is a longitudinal sectional view of one '40" form of fuse-plug embodying. my invention.

Fig. 2 is a transverse sectional view on the plane of the line 2--2 of Fig. 1.

Fig. 3 is a front end view of the plug.

Fig. 4 is a drop or exploded perspective view showing the various parts of the plug.

The base which is preferablyof porcelain or other-suitable insulating material has a disc-like portion 5, a boss 6, a sleeve or collar 7, and a longitudinal passage 8.

The fuse link may be formed of any suitable material and has a transverse portion 9 whichbears the fuse rating, such as Amp., printed or stamped in any suitable manner; This link has two legs 10 and llwhich serve to-support it. and it may have oneor more contracted portions such as 10' as is common in such constructions. One end 10 is adapted to be connected to the center' contact and the other end 12 is adapted to engage the screw shell contact.

The screw shell 13 is of the usual character provided with a flange 14 through which the boss 6 projects when the parts are assembled. This flange 14-surrounds the edge of the disc portion 5- of the-base.

The center contact 16 is in the form of a hollow rivet into which the end 10 of the fuse link is inserted and held by an expanded pellet or solder 17; The other end 12 of the fuse link is soldered at 18 to the screw shell when the parts are assembled.

The top or outer end of the fuse plug is formed of glass and has a cylindrical portion 19 with achamber 20, a transparent outer end 21 preferably in the form of a magnifying lens, and a flange-or hand hold 22 for convenience in gripping; the plug. The portion 19 is threaded to receive the outer edge of the screw shell 13 and is providedwith groove 23 into which the tip 12 of the fuse link may be bent and soldered to the screw shell 18.

It will be understood, of course, that a reasonable amount of clearance exists between the parts so as to permitthe relief of gas pressure due to blowing of the link.

While the construction such as shown has considerable-commercialadvantage the glass even when made of a high resistant character becomes so hot when the fuse blows that it can not be handled with the bare hands. In fact even when made of a composition such as that commonly termed Pyrex the glass cracks and creates a hazard contrary to modern safety requirements.

I have discovered that by the use of a thin layer or coating 25, of a composition such as water glass, these difficulties may be entirely eliminated. This coating is preferably applied over the inner face of the outer transparent or lens portion of the glass but may also be applied around the sides as indicated in Fig. 1. Such material in fact if applied in sufficient quantity around the sides may accomplish substantial advantageous results.

The exact composition is not critical for the accomplishment of the desired result but I have found that a solution having the approximate proportions of thirty percent SiOz and nine percent NazO' and a specific gravity of approximately forty degrees Baum is satisfactory. This composition is liquid at normal atmospheric conditions when properly preserved but soon hardens varying degrees of success dependent on the relative perfection of the construction to which it is applied. 7 a

The form shown herein has successfully withstood the most rigid tests applied in accordance with the requirements of the fire underwriters.

Although the additional cost entailed by the use of the protective coating is extremely small the results attained are striking.

The exact explanation of the phenomenon is not altogether clear. 'It is apparent, however,

that the material employed should be substantially transparent and easily applied as for instance in a solution capable of drying in a reasonable time. While it is possible to use powder in such a construction in addition to the protective coating it is unnecessary.

When the fuse blows the material,usually containing zinc, is of course burned up and the oxide formed. It is possible that the zinc or the oxide may react with the sodium silicate. It is also likely that the driving off of the water from the coating absorbs sufiicient heat units to materially keep down the temperature of the glass. Suffice to say, however, that the results obtained by the use of the coating in a construction of the character described are astonishing.

. The insulating barrier 7 which extends almost to the outer end of the fuse-containing chamber and close to the side wall of said chamber serves as a protection barrier to closely confine the leg 11 of the fuse strip between the inner wall of the body and the outer wall of the barrier 7 and to choke off the arc which forms when the fuse blows and thus prevents the development of high temperature and high pressure which would tend to explode or fracture the glass. In fact this construction is practically non-shatterable under the usual conditions of use.

I claim: I

1. A fuse plug comprising a body having a recess, a top having a wall surrounding the recessed partof the body and having a transparent portion in line with the recess, a transparent water-containing coating within the top, a center contact on the body, a screw shell contact uniting the body and top and a fuse strip having one end connected to the center contact and the other end connected to the screw shell.

2. A fuse plug comprising an insulating body, contacts carried by said body, a glass top having a chamber and a transparent outer end, a water glass coating on the inner surface of said transparent outer end, a fuse strip visible through said outer end and through said coating and having its ends connected to said contacts.

3. A fuse plug including a transparent glass top having a chamber, a fuse link mounted in said chamber and visible through said top, and a coating of a transparent composition within said chamber in a region to coact with the fuse arc and prevent fracture of the glass when the fuse blows, said transparent composition permitting the condition of the fuse link to be seen through the glass top.

that the invention may be applied to various constructions perhaps with- 'of the glass when the projecting into the chamber in the body, a contact at the end of the base, a metallic shell securing the body and base together, a fuse strip having one end secured to said contact within said sleeve and the other end connected to the shell, the central portion of the strip being visible through said transparent end of the body and a layer of a transparent reinforcing material inside the glass body between the fuse strip and the glass.

5. A fuse plug comprising a transparent glass body having a tubular portion with a lens at its outer end and threaded exteriorly, means for rendering the lens shatter proof, an insulating base having a flange closing the inner end of the tubular portion and having an insulating barrier portion extending from the flanged end of the base and close to the inner wall of thetubular portion of the body and to a point adjacent the lens portion of the body, a screw shell terminal embracing the threaded portion of the body and the flange of the base to hold the base to the body, a center contact member extending through the base, a fuse strip having its inner end secured to said center contact member and having its central portion extending across inside the tubular member to be viewed through said lens and having one leg confined between the inner wall of the body and the outer wall of said barrier, the outer end of the fuse strip passing between the end of the tubular portion of the body and the flange of the base and secured to the screw shell.

6. A fuse plug comprising two members having a chamber between them, the outer member being formed .of transparent glass with a finger grip, the inner member being formed of insulating material, a screw shell uniting said members and constituting an outer contact, a center contact carried by the inner member, a fuse strip connecting the two contacts and visible throughthe glass and transparent means for reinforcing the glass top and rendering it shatterproof, said transparent means containing water which is driven off when the fuse has blown.

'7. A fuse plug having a vented chamber and including a transparent glass top, a fuse link mounted in said chamber and visible through.

said top, and a coating of a transparent composition on the glass within said chamber in a region to coact with the fuse arc and prevent fracture fuse blows, said composition changing chemically when the fuse blows.

8. A fuse plug comprising an insulating body member, contacts carried by said body, a glass top member having a transparent outer end, a water glass coating on the inner surface of said transparent outer end, a fuse strip visible through said outer end and through said coating and having its ends connected to said contacts, and a tubular guard surrounding at least a part of the fuse strip. 7

9. A fuse plug comprising a body having a recess, a top having a transparent portion in line with the recess, a transparent water-containing coating within the top, a center contact on the body, a screw shell contact uniting the body and top and a fuse strip having one end connected to the center contact and the other end connected to the screw shell and visible through said top and coating.

10. A fuse plug comprising an insulating body mounted in said chamber and visible through said top, and a coating of water glass on the glass Within said chamber in a region to coact with the fuse arc and prevent fracture of the glass when the fuse blows, said composition being changed chemically by the heat due to the blowing of the fuse.

GEORGE R. 'I'RUMBULL. 

